My invention relates to a technique for providing gray tones and color on an ac plasma panel.
A plasma panel is a display device comprised of a body of an ionizable gas sealed within a nonconductive transparent envelope. Images on the device are displayed by controllably initiating glow discharges at selected locations within the displayed gas. This is accomplished by setting up electric fields within the gas via appropriately arranged electrodes or conductors.
The invention relates to so-called twin substrate panels where the electrodes are imbedded within dielectric layers disposed on two opposing nonconductive surfaces, such as glass plates. Typically, the conductors are arranged in rows on one plate and columns orthogonal thereto on the other plate. The overlapping, or crosspoints, of the row or column conductors define a matrix of discharge cells or sites. Glow discharges are initiated at selected crosspoints by application of a particular voltage pulse. At any site, the continual reversal of voltage polarity will result in a sustained discharge at that site.
The voltage across the site creates a space charge cloud of electrons and positive ions in the region of the site. In a typical ac plasma panel, concomitant avalanche multiplication, as a result of the applied voltage, creates a glow discharge and an accompanying short (i.e., one microsecond) light pulse in the visible spectrum. The control of an ac plasma panel is, for example, shown in my copending patent applications, Ser. Nos. 109,859, filed Jan. 7, 1980, and 307,169, field Sept. 30, 1981, and which are hereby incorporated by reference.
One major problem with ac plasma panels is their relative inability to provide light intensity control at a discharge site and an inability to provide a full color display. Thus, problems arise from the on-off nature of plasma panels where the monochromatic color of the display is dependent upon the type of gas being ionized with the intensity of the emitted light also being a function of that gas. Thus, while ac plasma panels find widespread acceptance for graphic displays, they have not been found to be acceptable for applications, such as for example, television, where a high degree of contrast is necessary or where color presentation is desirable.